Cold forging process



July 11, 1961 H. B. CHATFIELD 2,991,552

Y COLDIFORGING PROCESS Filed Aug. 14, 1957 2 sheets-sheet 2 INVENTOR Henry B Chat'ield ATTORNEYS nited gratas Y 2,991,552 y YCOLD FORGING PROCESS Henry B. Chatiield, Kinsman, Ohio (13.0. Box 7, Orangeville, Ohio) p Filed Aug. 14, 1957, ser. No. 678,176 3 Claims. (Cl. 29-556) The present invention relates to an improved method f cold forging or coining metal.

It is elemental that metal deforms as load is applied to it. The initial deformation is within the elastic limit of the metal or temporary deformation in that the metal returns to its initial shape when the load is released. Subsequent deformation is beyond the elastic limit of the metal or permanent deformation. The point at which the metal commences permanent deformation is the yield point. The tensile strength is the apparent stress at fracture or break.

All cold forging takes place between the yield point and break. With the more ductile materials, this range is relatively large. For example, the yield strength of most low carbon steels is from 40-50,000 p\.s.i. and the tensile strength is from 70-80,000 p.s.i. Tool or die steels, on the other hand, have yield strength of 275- 350,000 p.s.i. and only slightly higher tensile strengths. The stresses or unit loads in cold forging have to be kept below the yield strength of the tool steel and above the yield strength of the metal being forged.

I have devised a method of cold forging in which the stresses are maintained in the lower range of the spectrum and stress concentrations are avoided or minimized.

One object of the present invention is to provide a method of cold forging metal in which the unit loads are kept well within the elastic limit of the tool steel and within the tensile strength of the metal being forged.

Another object of the present invention is to provide a method of cold forging which can be adapted to a variety of parts.

Other objects and advantages will become apparent from the following description and accompanying drawings, in which:

FIGURE l is a perspective of a blank used in a sequence illustrating the present invention.

FIG. 2 is a cross-sectional view of a punch and die with the blank of FIG. l therein just prior to initial contact between the punch and blank.

FIG. 3 is a cross-sectional view similar to FIG. 2 at the point of initial contact between the punch and blank.

FIG. 4 is a cross-sectional view partially progressed from FIG. 3 above showing the metal flow of the blank.

FIG. 5 is a `cross-sectional view still further progressed from FIG. 3 above.

FIG. 6 is a cross-sectional view showing the punch at completion of the forging operation.

FIG. 7 is a plan view of the forged piece removed from the die of FIG. 6.

FIG. 8 is a cross-sectional view of the piece of FIG. 7 with the iiash ring removed, and

FIG. 9 is a perspective of the forged piece with the ash ring removed.

In accordance with the present invention, I correlate the design of the punch, die and metal blank so that as the punch descends on the die, the major portion of the forging force is applied about the edges or periphery of the die cavity to pinch the metal blank and cause lateral metal ow both inward toward the center of the blank and outward toward the edge. I call this doubleow pinch. 'Ihe resultant metal flow forms bulbous portions about the periphery of the blank and enlarges the center of the blank so as to lill up the die cavity.

Patented July il, i961 rice As the punch continues to descend, the edges of the blank are pinched closer and closer together until a point is reached at which there is no metal ow, the mold cavity is lled up, and the article is molded to shape with a thin flash about the edge. The fact that the metal flows both ways from the center of the ash holds down the bursting pressures. More particular' ly, the lateral inward metal flow neutralizes or prevents the build-up of lateral outwardly directed bursting forces on the tooling such as are obtained with conventional techniques. The metal of the iiash is work-hardened and is readily broken or tumbled off. This leaves a thin, peripheral line on the coined article which causes no harm but may be touched up, if desired, by emery cloth, light grinding, or other finishing operations.

The drawings illustrate the process in further detail as applied to the cold forging of the cam 5 shown in FIG. 9.

The original blank is shown in FIG. l and comprises a ilat, `cylindrical-shaped piece ll with an upstanding center portion or boss 2. This piece may be made on a cold heading machine from cold rolled '1040 stee rod or the equivalent.

FIG. 2 shows the piece mounted on the die or anvil 3 prior to any deformation. The die 3 and punch 4 are provided with Hash-forming land portions 6 adjacent and outward from the forming cavity so as to create the greatest unit pressures at the edge portions of the blank and cause lateral metal ow toward the center of the cavity to ll it up. The die and punch adjacent the land portions are relieved as shown so as to facilitate and control lateral outward flow of the metal and provide the necessary pinching effect. The die is provided with a cavity 7 corresponding in shape and configuration to the lower portion of the article being cold forged. Punch 4 likewise has a cavity 3 which conforms to the upper portion of the article being cold forged. Cavities 7 and 8 define the shape of the article being forged and constitute the forming cavity 21 (FIG. 6).

FIG. 3 shows the operation after initial contact has been established. Here the flash-forming ring or pinching land 9 of the punch and similar and complementary ring 10 of the die are just engaging the metal of the blank adjacent and outwardly from the edges of the forming cavity so as to apply the pinching force thereto. While the inner shoulder 11 of the punch also engages the circumferential edge portions of the boss 2 of the blank the greatest unit pressures are created slightly in from the edges of the blank as shown and between the edges of the blank and edges of the forming cavity.

In FIG. 4 the peripheral portions of the metal blank have been further compressed and forced to move laterally in toward the center of the blank to ll up the forming cavity and out toward the periphery of the blank to form the outer flash ring 12. The flow of the metal is shown by the arrows. The outward metal ow is controlled by outwardly tapered portions 13 of the punch and 14 of the die. As is readily apparent, the taper may be changed and made greater or smaller so as to conne outward flow or provide more easy relief and help neutralize tool bursting pressures.

FIG. 5 illustrates the operation as the punch has advanced still ftuther toward the die and is approaching the bottom of its stroke. At this stage, lateral metal iiow is slowing down andthe operation is nearing termination. The operation terminates when inward and outward metal ow at the flash or pinched area stops. The edges 17 and 1S of the shaft portion of the piece are not fully formed but otherwise the piece substantially conforms to the cavities.

As the thickness of the flash portions decreases, lateral metal ow requires rapidly increasing tonnage because of the frictional resistance to flow of the surface portion of metal contacting the lands. There is a definite surfaceeifect limiting factor so that beyond a certain thinness of the flash portions there will be no metal flow even with excess pressures on the tools.

FIG. 6 shows the punch at the bottom of its stroke. The forming cavity defined by the punch and die is completely filled with metal. There is a thin flash formed adjacent the peripheral edges of the cavity. Because of the metal flow both ways from the center of the pinch at the flash line the cavity has been completely filled giving accurate definition in all recesses without generating excess bursting stresses in the cavity which would otherwise cause early if not immediate tool failure. Thus in accordance with my invention it is only necessary to control the thickness of the blank and the angle of the exterior ash pinch on the die to control both the dimension of the finished part and the bursting stresses on the tools.

The flash portion may be as thin as .005 but generally it is from .0l to .06" thick and it may be up to .10" thick, depending upon the metal being forged and the thickness of the adjacent metal. 4It can be 1/3 the thickness of the blank or thinner. The metal in the flash portion is work-hardened and brittle so that the flash portion can readily be broken off by hand, tumbled oi or otherwise removed.

FIG. 7 shows a plan view of the forged article removed from the punch and die with the flash ring 12 still attached. This corresponds to the article of FIG. 6 at the bottom of the stroke. The circumference of the original blank is shown in dotted line as a comparison with the original shape. FIG. 8 is a cross-section taken along line 8 8 of FIG. 7 with the yflash portion and flash ring shown in dotted lines. FIG. 9 is a perspective of the finished part after the flash has been broken away. In this instance the part is a cam but, of course, many other parts and shaped articles may be manufactured by the process of the present invention.

The major force of the punch should contact and apply forging forces to the blank around the peripheral edges of the cavity as shown and not the center portions of the blank as in conventional coining and forging operations. In other words, during the initial stages of the coining operation, the metal ow should be in a lateral direction from both sides of the neutral axis 16-16 adjacent the edge of the cavity. There is no attempt to contact the center portions of the blank and squeeze metal out through the slot formed about the peripheral portions of the cavity. The operation may be considered as an extrusion in which metal Hows into the forming cavity and flash ring `from the blank portions adjacent and outward from the edge of the forming cavity. It should be noted that the extrusion is from a smal-l space into a larger space or is at least 1 to l so that the stress is relatively low and not concentrated.

In order to apply the principles of the present invention, it is not necessary to have ash forming land portions in both the punch and die. The die may be a ilat platen or merely have land portions correlated with the edge of the cavity in the punch. Likewise, in some applications, the punch may be flat and not have a cavity or land portions formed therein. In accordance With the present invention the important feature of the punch and die is that both be formed and correlated so as to pinch the metal of the blank being worked up about the periphery of the forming cavity so as to bring about lateral flow of metal towards the center of the cavity.

The movement of the metal is shown by the arrows in FIGS. 4 and 5. The metal should be considered more as a plastic material than a solid in that the application of force to the metal blank seems to create internal pressures which act normal to the confining surface, as in a plastic.

'I'he metal moves laterally away from neutral axis 16-16 shown in FIGS. 4 and 5. This axis is representative only and is determined from analysis of grain structure taken from blanks in various stages of the operation. 'It should be noted that the neutral axis is not stable and moves laterally during the operation. The neutral axis 16I6 of FIG. 4 is closer to the center of the blank than that of FIG. 5.

The starting blank must have greater lateral dimensions and at no point be substantially thicker along the axis of reciprocation of the punch than the `forming cavity. The sequence of operations should be worked out so that as the operation reaches completion, the forming cavity is almost filled and there is no excess of metal which has to be forced laterally outward. By controlling the thickness of the starting blank, the operation can be worked out so that the above result is achieved. If the forming cavity is not filled at the bottom of the stroke of the punch or at the stage of the operation corresponding to FIG. 6, the blank should be slightly thicker. If there is too much metal and a tendency to force metal laterally outward through the punch and die land portions, the blank should be slightly thinner. In this manner, very accurate control can be achieved without imposing severe strains on the tools.

If for any reason the thickness of the metal blank cannot be controlled, the force applied by the press can be limited so as to achieve a similar result. With a hydraulic press, the maximum pressures can be controlled and the punch retracted when the predetermined pressures are reached. With a knuckle-joint or other mechanical press, a similar result can be achieved by stroke limiting bars placed on the platen. In each case, the forging operation is stopped before excessive bursting forces are developed in the tooling. Control of press pressures instead of blank thickness results in some loss of tolerances but is otherwise equivalent.

The amount of lateral metal flow and degree of punch is controlled in part by the design of the flash-forming land portions and the relieved outer tapering portions thereof. inward and outward metal flow is complementary in that when the metal is pinched by the land portions, it has to flow laterally one way or the other and the metal will follow thepath of least resistance to flow. Thus when there is not enough lateral inward flow, out- Ward ow is limited yand vice versa. lf the outer taper is extreme so as to open out rapidly from the flash portion, outward metal flow is facilitated. If the taper is gradual so as to open out slowly from the ash portions, outward metal ow is hindered. The angle and degree of taper or relief of the flash-forming lands act as a valve and can be used to limit outward metal flow or encourage it, as the particular job requires. This angle may also be varied about the periphery of articles as necessary to control metal flow. Generally, it is not necessary except where the part itself is irregular in plan shape. The flash ring or outer annulus integral with the ash portion is thus free-form in the direction lateral to the forging forces and, depending upon the taper, may be free-form to a greater degree.

As used herein, the term lateral means the direction at right angles to the axis of reciprocation of the punch. Since most punches reciprocate on a vertical axis, the lateral direction is the horizontal direction.

.The subject process may be adapted to any of the metals which are generally cold forged and for some parts may utilize metals not presently cold forged. Low carbon steels, brasses, copper and stainless steels are examples of metals which are cold forged in accordance with the present process. Titanium alloys and some of the other so-called super alloys are examples of metals which can be forged in accordance with the present process but which are not generally cold forged. Naturally, much of Whether a super alloy part can be cold forged or not depends upon its shape and specifications.

1li t9 b@ lllldrSQOd that in accordance with the provisions of the patent statutes, the process is not limited to manufacture of the specific part herein shown and described and variations and modications of the invention may be made without departing from the spirit of the invention.

What I claim is:

1. A method of cold forging metals in a punch and die that together define a forming cavity comprising the steps of disposing a suitable metal blank on the die so that the edges of the blank extend laterally beyond the edges of the forming cavity in the punch and die, said blank having a central portion with an amount of material therein greater than the amount of material required to fill the corresponding central portion of the cavity defined by the punch and die bringing the punch down upon the blank so as to apply compressive force about the edges of the cavity and outwardly therefrom and to pinch the metal between the punch and die to provide sutiicient metal flow laterally in toward the center of the cavity and away from the center of the cavity to fill up the cavity with metal and leave a thin metal flash about the edge of the article in the forming cavity, retracting the punch, removing the article, and then removing the ash from the article formed by the forming cavity to provide a nished article, said blank having a larger volume than said forming cavity and at no point being substantially thicker than said forming cavity so as to permit pinching the edge portions thereof and lateral inward metal flow.

2. A method of forging an article from a metal blank in the cold state comprising the steps of disposing a suitable blank between a punch and a die, which blank has a greater volume than the cavity formed by the punch and die, is at no point substantially thicker than said cavity and extends laterally beyond the edge of said cavity, causing said punch to close on the die so as to create the greatest unit pressures in said blank adjacent and outwardly from the edge of said cavity so that the metal of said edge portions extrudes laterally in toward the center of the blank and laterally outward therefrom until the metal of the blank completely lls the cavity and a thin work-hardened metal flash and integral outer annulus is formed about and outwardly from the edge of the cavity, withdrawing the punch, and then separating the ash and free-form annulus from the article lling said cavity to obtain the finished article.

3. A method of cold forging metals in a punch and die which together deine a forming cavity comprising the steps of disposing on the die a metal blank which is at no point substantially thicker than the forming cavity, is generally of the same conliguration as the forming cavity, and has a larger overall volume than the volume of the forming cavity so that the edges of the metal blank extend laterally beyond the edges of the forming cavity, bringing the punch and die together to apply compressive forces to the metal blank about the edges of the forming cavity to pinch it in that area and provide enough metal flow laterally in toward the center of the forming cavity to ll it up completely with metal and form a thin workhardened dash in the metal blank about the edges of the forming cavity, separating the punch and die, removing the article so formed from between the punch and die, and then removing the thin -tiash from the article so formed to provide a cold forged article corresponding in shape to the forming cavity.

References Cited in the tile of this patent UNITED STATES PATENTS 774,242 Gates Nov. 8, 1904 1,331,921 Heiby et al. Feb. 24, 1920 1,373,725 Heiby et al. Apr. 5, 1921 1,397,566 Walter Nov. 22, 1921 1,434,190 Bird Oot. 31, 1922 1,726,180 Habenicht Aug. 27, 1929 1,935,516 Musgrave Nov. 14, 1933 2,057,669 Brauchler Oct. 20, 1936 2,201,225 Cadwallader May 21, 1940 2,305,803 Bayer Dec. 22, 1942 2,345,343 Keller Mar. 28, 1944 2,393,628 Goldie et al Jan. 29, 1946 2,786,267 Chappuis Mar. 26, 1957 

